Photopatterned Anchoring\nStabilizing Monodomain Blue\nPhases

Blue phase liquid crystals (BPLCs) are chiral self-assembled\nthree-dimensional\n(3D) periodic structures which have attracted a lot of attention due\nto their electro-optical properties, relevant for tunable soft photonic\ncrystals and fast-response displays. However, to realize this application\npotential, controlling the BPLC alignment at the surfaces is crucial,\nand one way to obtain the desired alignment is by photoalignment patterning.\nIn this article, monodomain BPLC samples with controlled orientation\nare achieved by imposing different alignment patterns that have a\nperiodicity that is compatible with the size of the BPLC unit cell,\nusing two-step photoalignment with polarized ultraviolet (UV) light.\nExperiments are complemented by numerical simulations to design striped\nsurface alignment patterns, which induce specific director orientations\non the boundary layer of the confined BPLC. By designing the patterns\nand matching the periodicity to a specific BP material, we can control\nthe orientation of the blue phase unit cell lattice in the sample,\nincluding the azimuthal angle. The orientation is measured by the\nKossel patterns and matches the optimal configuration predicted by\nstability analysis using Landau–de Gennes free energy modeling.\nThe detailed structure and reduced symmetry of the BP near the surface\nare investigated, and the corresponding (meta)stable structures are\ndemonstrated. Overall, we demonstrate that two-step photoalignment\npatterning is a reliable, relatively simple, and reconfigurable method\nto achieve a high-quality monodomain BP with controlled and tunable\ncrystalline orientation.